3 week old duckling won't eat or socialise with new flock

I am hoping someone can provide some advise.
We live in the tropics and got 10 baby ducklings around 10 days old. Unfortunately a few days later; local dogs killed all but one chick.
We took in the surviving chick so it would be in the back of our house during the day and in the night in our shower room.
As days went by; his personality developed; ate well and was a joy. In the afternoons we would take him out for small walks and he would sit next to my husband at his work desk before placing him in the shower room for the night.

A few days ago, we received another 9 ducklings around the same age. Everything seemed ok; he was curious of the others for the first day; then day after; he started to keep himself apart from the other chicks; and now has stopped eating.
We are trying to force feed him but not working very well.

Worried he will get too weak and die which would be tragic after surviving a dog attack.

Living in a tropical island, we don't have pet shops or vets; he has been eating paw paw, banana; avocado and the occasional egg.
Always plenty of water on hand.

Can anyone tell us what is happening and if we can fix this situation before he gets any weaker.

I'm a little confused, are these chicks or ducklings? You say both. I think you mean you have ducklings though.

My first though would be that what you are feeding them isn't cutting it. They really do need to be on feed. Just bananas and eggs and fruit isn't an adequate diet. They need a lot of protein to sustain their growth, and they grow fast so they need a lot. What would you feed chicks if you had chicks there? I know you said you're on an island but can you get a chick feed? Where do people go to get feed for livestock? That would be where you'd need to go to get chick feed. Can you find out what others on the island feed their ducklings and chicks and feed them that? Or order some chick feed in for them if you can't get any on the island?

The other problem is if you get a chick feed, it won't have enough niacin for ducklings. Ducklings require more niacin than chicks do, and since you're on an island it might be hard for you to find chick starter, let alone duckling starter. So you'll need to add supplemental niacin to the feed. Order some Brewer's yeast if you can to add to their feed or water so they get the amount of niacin they require.

Thank you for taking the time to respond; really appreciate it.
I'm sorry about the confusion; I don't usually subscribe to anything on-line, but getting a little desperate about this duckling.

Yes, they are ducklings, not chicks.

I'm in Vanuatu and live on the island of Tanna. Very basic island inhabitants; no supermarkets, or vets or pets!
Not many white people here either.

We have been living in Vanuatu for 16 years but originate from Australia.

We are now in the process of building a resort on Tanna and one of the things we want to introduce are ducks.
People on this island don't have pets or understand what it is to love and care for animals. To the local person, a dog is something you have for village protection. A chicken roams free; not fed and disappear all too often (dogs are starved so chickens are a quick meal)

I can order brewers yeast from the main island of Efate and have it flown in.
There is one vet in the entire country and is located on Efate, but would be more familiar with dogs, cats and horses!
If anyone has ducks, it would be mainly in remote areas; free ranging on homesteads with no special attention.

The ducks were sent to us from Efate by an acquaintance who has drakes and ducks; they breed alot, so sold a few ducklings. The ducks and offspring forage around the property. We were told they would forage in the grass and go after insects and left overs.
We tend to look after animals in our care so wanted to do the right thing and grow healthy, happy animals.

Vanuatu is not a place where animals are high on the list of caring. Expats have dogs, and cats, but not common to have ducks!

Have been reading as much as I can find. Unfortunately not much on the net about ducklings.

Have read they can be fed cut up grass, herbs, peas, and a variety of vegetables and some fruit. Will introduce this to these little fellows and see how we go.

Just thought there may be an answer as to what is happening with our little survivor.